1. Field of the Invention
The present invention relates to an ink jet recording device capable of forming high-quality images at high speed by using a plurality of print-head modules.
2. Related Art
There has been proposed a serial-scanning type ink jet recording device including a recording head that forms dot images on an elongated recording sheet by ejecting ink droplets while scanning in a widthwise direction of the recording sheet. Specifically, the recording head produces, during a single scan, one-line worth of image, which includes a plurality of primary scanning lines. Then, the recording sheet is transported in its longitudinal direction, which is perpendicular to the widthwise direction, by a predetermined distance. Then, the recording head forms a next one-line worth of image. These operations are repeatedly performed, so that a whole image is completed.
In order to improve the image forming speed, the number of primary scanning lines that the recording head prints in a single scan may be increased. In this case, the recording head is configured to have a relatively large length in the lengthwise direction so that an increased number of nozzles, through which ink droplets are ejected, are formed thereto.
In another type of ink jet recording device, a recording head has a large width equivalent to an entire width of the recording sheet such that nozzles are formed for every one of a plurality of secondary scanning lines that extends in the longitudinal direction of the recording sheet. With this configuration, the recording head can form a complete image without moving in the widthwise direction at all.
There are various methods for producing this type of recording head with such a wide width. In one method, a line of a plurality of nozzles is formed to a wide-width recording head at once. However, in this method, if even only one of the nozzles is formed to have an irregular ink-ejection characteristics, quality of a whole image is greatly degraded, so this method requires a relatively high production cost.
In another method, a plurality of short-width head modules each formed with a plurality of nozzles are assembled to produce a single wide-width recording head. That is, a complete image is formed by a combination of a plurality of image-portions, which are formed by corresponding head modules. Because the short-width head modules are formed at a lower cost, the entire production costs can be reduced. However, this method requires an accurate assembly of the head modules.
Japanese Patent Application Publication (Kokai) No. HEI-9-262992 discloses a conventional method for accurate assembly of the head modules. In this method, actual printing is performed, and location information of each head module with respect to the widthwise direction is obtained. Then, based on the location information, the head module is mechanically moved to a proper position if there is any undesirable positional error. This mechanical movement is performed by using an adjusting unit.
Positions with respect to the lengthwise direction can be mechanically corrected in the same manner. However, with respect to the lengthwise direction, the positional error can be electrically corrected by using adjustment recording data, so a combination of mechanical method and electrical method is used for correcting the positional error of the head modules.
However, the above conventional method requires a complex adjusting unit to improve the accuracy of the positional adjustment. Also, automatic mechanical adjustment is not possible.
It is an objective of the present invention to overcome the above problems and also to provide an ink jet recording device including a plurality of head modules and capable of printing a high-quality image at a high speed rate and automatically and electrically correcting positional relationship among dot groups that are formed by the head modules.
In order to achieve the above and other objectives, there is provided an ink jet recording device including a plurality of head modules, a moving mechanism, ejection means, deflection means, and correcting means. The plurality of head modules are assembled side by side in a widthwise direction for forming dot groups on a recording medium. The dot groups are aligned in the widthwise direction to form a complete image. Each of the plurality of head modules is formed with a nozzle line extending in a line direction and including a plurality of nozzles through which ink droplets are ejected to form the corresponding dot group by forming corresponding dots on the recording medium. The moving mechanism moves the recording sheet relative to the plurality of head modules in a moving direction at an angle xcex8 with respect to the line direction. The moving direction is perpendicular to the widthwise direction. A plurality of first scanning lines extending in the moving direction are defined on the recording medium. The ejection means selectively ejects ink droplets from the plurality of nozzles in an ejection direction at an ejection timing. The deflection means deflects the ejection direction of the ink droplets toward a deflection direction perpendicular to the line direction by one of predetermined deflection amounts. The correcting means corrects positional error of the dot groups. The correcting means includes first control means for controlling the predetermined deflection amounts so as to form the dots on the first scanning lines and second control means for controlling the ejection timing so as to adjust positions of the dots with respect to the moving direction.
In this configuration, there is no need to provide an additional separate unit for mechanically correcting head module assembly. The correction can be performed automatically by electrical means.